Preheat oven to 400º F. Spray an 8x8 pan with cooking spray and set aside.
In a mixing bowl, combine the Bisquick, sugar, egg, milk and 1 Tbsp. of the melted butter, and the vanilla. Mix with wooden spoon until smooth. Pour into prepared pan and smooth down the top.
Mix brown sugar and cinnamon in a small bowl. Drizzle remaining butter over the top of the coffee cake and sprinkle cinnamon and sugar mixture over the butter. Lightly swirl batter with a knife for a marbled effect.
Bake in preheated oven for about 20 minutes, or until a toothpick comes out clean. Slice up and enjoy!